Safety Brake Device

ABSTRACT

A safety brake device for braking a machining tool includes at least one brake device configured as an at least two-part claw clutch. The claw clutch includes a first claw-clutch part, and a second claw-clutch part. The first claw-clutch part is arranged on the output shaft so as to allow no relative rotation, the second claw-clutch part is configured to allow no relative rotation with respect to the power tool, each claw-clutch part has a respective plurality of toothing elements, the respective plurality of toothing elements are configured to engage with one another during a braking operation to stop rotation of the output shaft, and a maximum angular spacing Δmax of mutually adjacent toothing elements of at least one of the first plurality of toothing elements an the second plurality of toothing elements is determined depending on a maximum rotational speed of the output shaft.

The invention relates to a safety brake device for a power tool.

PRIOR ART

Safety brake devices are known from the prior art, for example from DE10 2008 054 694 A1.

DISCLOSURE OF THE INVENTION

The invention proceeds from a safety brake device for a power tool forbraking a machining tool driven by means of a motor via a shaft when auser approaches or comes into contact with the machining tool. Thesafety brake device has at least one brake device which is configured asan at least two-part claw clutch (or equivalent: claw brake) with afirst claw-clutch part and a second claw-clutch part, wherein the firstclaw-clutch part is arranged on the shaft so as to allow essentially norelative rotation, in particular also so as to be axially movable, andwherein the second claw-clutch part is provided to be arranged so as toallow essentially no relative rotation, in particular so as to besubstantially immovable, with respect to the power tool, and the firstclaw-clutch part and the second claw-clutch part each have more than onetoothing element, wherein the toothing elements are provided to engagewith one another during a braking operation and in such a way to brake,in particular stop or block, rotation of the shaft.

A “safety brake device” is intended to be understood in particular asbeing a device that brakes or stops a machining tool by means of atleast the brake device in a situation in which the machining toolrepresents a hazard to a user. In particular, the safety brake devicebrakes the machining tool when a user approaches or comes into contactwith the machining tool. In one embodiment, the safety brake device alsocomprises a processing unit and a sensor unit, wherein the processingunit communicates with at least one sensor of the sensor unit, whereinthe sensor is provided to detect a hazard to a user, in particular theuser approaching the machining tool and/or the user coming into contactwith the machining tool. Electronics of the safety brake device canthen, following detection of the user approaching the machining tooland/or following detection of the user coming into contact with themachining tool, trigger for example an actuator element, which triggersa braking operation using the brake device. The actuator element can berealized in particular as a constituent of the brake device orseparately therefrom. The actuator element can, in one exemplaryembodiment, be in the form of a lifting unit, which actively moves atleast one of the two claw-clutch parts of the claw clutch in order toengage the two claw-clutch parts with one another during a brakingoperation and in this way to brake, in particular stop, rotation of theshaft. Such actuator elements are known to a person skilled in the artfrom the prior art. Active movement of at least one of the at least twoclaw-clutch parts can be realized in this case for example by a leverelement, a spring element, a transmission element or the like.

The term “provided” is intended to be understood in particular asmeaning especially equipped, designed and/or programmed.

A “power tool” is intended to be understood as meaning in principle anypower tool that has a rotatably mounted machining tool driven by meansof a motor via a shaft, in particular an output shaft. The machiningtool can also be realized in particular as a tool receptacle. Themachining tool is connected to the output unit so as to allowessentially no relative rotation or is connectable to the output unit soas to allow essentially no relative rotation at least in an operatingstate of the power tool, for example via a tool receptacle, such that atorque is transmissible from the output unit, in particular the outputshaft, to the machining tool. The expression “so as to allow essentiallyno relative rotation” should be understood at this point as meaning thatthe machining tool executes a relative rotation of less than 15°, inparticular of less than 10°, very particularly of less than 5°, withrespect to the output unit during a braking operation. The torque isgenerated by a drive unit, for example an electric motor, in particulara brushless DC motor (EC motor), and/or some other motor that appearsappropriate to a person skilled in the art. The shaft, in particular theoutput shaft, can be connected to the drive unit using a transmission ora clutch or without such connecting elements. Examples of such powertools include in particular drilling machines, string trimmers,lawnmowers, circular saws, bench saws, cross-cut saws, miter saws, orother power tools that appear appropriate to a person skilled in theart. In one embodiment, the power tool can be realized as a portablepower tool, for example a cordless battery-operated portable circularsaw or the like. In one embodiment, the power tool can be realized as aportable circular saw having a machining tool in the form of acircular-saw blade that is driven by means of a motor via a shaft, andhaving a sensor plate that senses contact of human skin with themachining tool.

A “shaft”, in particular an output shaft, allows the machining tool torotate by rotation of the shaft about its (axial) longitudinal axis.Typically, all other degrees of freedom, in particular a movement in aradial direction of a circular cross section of the shaft or in an axialdirection of the shaft, are prevented by the design.

A “brake device” should be understood as being a device that serves tobrake or stop the rotation of the machining tool in the event ofdetection of a user approaching or coming into contact with themachining tool. The brake device is realized according to the inventionas an at least two-part claw clutch (or equivalent thereto: claw brake).A “two-part claw clutch” should be understood as being a clutch thatfunctions by form-fitting coupling in that toothing elements on the twobrake device parts are brought into engagement with one another and thusallow torque transmission as a consequence of a relative movement of thetwo claw-clutch parts with respect to one another, in particular as aconsequence of a relative movement of the two claw-clutch parts in adirection of rotation with respect to one another. As a result of thesafety brake device being realized by means of a claw clutch, aform-fitting connection can be used to carry out a braking operation ina particularly quick and safe manner. The first claw-clutch part isarranged on the shaft, in particular on the output shaft, so as to allowessentially no relative rotation. In one embodiment, the firstclaw-clutch part can be arranged on the output unit in an axiallymovable manner or, in a further embodiment, in an axially immovablemanner. The second claw-clutch part is provided to be connected toanother constituent of the power tool, in particular for example ahousing, a transmission housing, a motor housing or some other structureof the power tool, so as to allow essentially no relative rotation, andthus to be arranged at least so as to allow essentially no relativerotation with respect to the power tool. In one embodiment, the secondclaw-clutch part can be provided to be connected to the otherconstituent of the power tool in a substantially immovable manner andtherefore to be arranged not only so as to allow essentially no relativerotation with respect to the power tool. In one exemplary embodiment,the second claw-clutch part is embodied in a substantially immovablemanner with respect to a motor housing of the power tool. In this way,in particular free rotation of the second claw-clutch part with respectto the power tool and also with respect to the shaft, in particular withrespect to the output shaft, and thus with respect to the firstclaw-clutch part, which is connected to the shaft so as to allowessentially no relative rotation, can be prevented.

The expression “so as to allow essentially no relative rotation” shouldbe understood as meaning that a respective claw-clutch part is mountedso as not to be substantially displaceable (rotatable) or able to slidein the direction of the circumference of the shaft, in particular of theoutput shaft. The expression “the first claw-clutch part is arranged onthe shaft so as to allow essentially no relative rotation” should beunderstood as meaning that the first claw-clutch part is connected tothe shaft, in particular the output shaft, so as to corotate with arotational movement of the shaft, in particular of the output shaft,wherein “substantially” means that a maximum relative movement of theshaft and first claw-clutch part with respect to one another is intendedto be allowed, which is less than 15°, in particular less than 10°, veryparticularly less than 5°. In one exemplary embodiment, the maximumadmissible relative movement of the first claw-clutch part is 12.5°. Inparticular, this relative movement occurs only when a very large torqueis applied to the first claw-clutch part, as can occur in the case of anabrupt braking operation.

The expression “the second claw-clutch part is arranged so as to allowessentially no relative rotation with respect to the power tool” shouldbe understood as meaning that a maximum relative movement of theconstituent of the power tool to which the second claw-clutch part isfastened, and of the second claw-clutch part with respect to one anotheris intended to be allowed, which is less than 30°, in particular lessthan 10°, very particularly less than 5°. In one exemplary embodiment,the maximum admissible relative movement of the second claw-clutch partis 15°.

The expression “axially movable/immovable” should be understood asmeaning that the first claw-clutch part is mounted so as to be movableor immovable, respectively, in the axial direction of the shaft, inparticular of the output shaft.

“Toothing elements” should be understood as being design-relatedprotrusions both of the first claw-clutch part and of the secondclaw-clutch part, which are provided to be brought into engagement withone another. Here, the toothing elements of one claw-clutch part form atthe same time recesses that receive toothing elements of the otherclaw-clutch part such that, upon interaction of the claw-clutch parts,protrusions (toothing elements) and recesses (depressions betweenadjacent toothing elements) form pairs that are arranged in acomplementary manner to one another. The toothing elements are broughtinto engagement in the event of a braking operation such that, as aresult of torque transmission between the (corotating) first claw-clutcharranged so as to allow essentially no relative rotation with the shaftand the second claw-clutch part arranged on the power tool so as toallow at least essentially no relative rotation with respect to theshaft, torque transmission is able to be generated, which counteractsthe rotational movement of the first claw-clutch part and in this waybrakes, in particular brakes or stops, the rotation of the shaft. In oneembodiment, the toothing elements are provided equidistantly and inparticular in such a way on the respective claw-clutch part that—withrespect to the axis of rotation of the shaft, in particular of theoutput shaft—they are arranged in a rotationally symmetric mannerthereto. In this way, an angular spacing Δ between adjacent toothingelements can be defined, wherein the angular spacing Δ represents theangle Δ, observed from the axis of rotation of the shaft, between thesetwo toothing elements. If two toothing elements are arranged for exampleopposite one another—with respect to the axis of rotation of theshaft—on a claw-clutch part, their angular spacing Δ is 180°. In thecase of an angular spacing of 360°, a claw-clutch part thus has only onetoothing element, whereas in the case of a respective angular spacing of180° there are two toothing elements and in the case of a respectiveangular spacing of 40° there are nine toothing elements.

The invention is based on the finding that, when designing the brakedevice of the safety brake device, a number and distribution of thetoothing elements—in particular with respect to a substantially circularcircumference of a respective claw-clutch part (defined by the directionof revolution of the toothing elements upon rotation of a claw-clutchpart)—is of significant importance, in order to achieve specificationsof a maximum tolerable reaction time of the brake device (braking time).

In particular, the angular spacing Δ between adjacent toothing elementsshould be chosen to be as small as possible for it to be possible toprovide a large number of toothing elements. The large number oftoothing elements makes it possible to reduce the rotational angle aboutwhich the shaft together with the first claw-clutch part has to rotateuntil two toothing elements of the first and the second claw-clutch partare engaged. The small rotational angle corresponds to a short brakingduration Δt (i.e. maximum tolerable braking duration or reaction time)until the two claw-clutch parts have been brought into engagement duringa braking operation. However, a large number of toothing elements alsocauses a small width of the toothing elements (in the direction ofrevolution) and thus reduced stability of the toothing elements. Inparticular, a width of the toothing elements that is too small canresult in a manufacturing process no longer being able to be carried outeconomically and/or in the toothing elements deforming or even breakingduring a braking operation. An optimized arrangement in terms of number,angular spacing and width of the toothing elements is thereforedesirable.

According to the invention, a maximum angular spacing Δ_(max) ofmutually adjacent toothing elements of the first claw-clutch part and/orof the second claw-clutch part is determined depending on a maximumrotational speed of the shaft, in particular of the output shaft. The“maximum angular spacing Δ_(max)” denotes in this case the greatestobservable spacing of two adjacent toothing elements—with respect to theaxis of rotation of the corresponding claw-clutch part and thus withrespect to the axis of rotation of the shaft, in particular of theoutput shaft. The “maximum rotational speed” of the shaft, in particularof the output shaft, is a parameter that is defined by the design andparameterization of the power tool. For example, the maximum rotationalspeed of an exemplary portable circular saw is 5000 revolutions perminute (rpm, corresponding to 83.3 revolutions per second (rps)). Thus,a brake device of the safety brake device, said brake device beingadapted specifically and particularly to the parameterization or designof the power tool, is proposed. In this case, the maximum angularspacing Δ_(max) of two adjacent toothing elements defines a maximumbraking time in the sense of a maximum “engagement time” of the toothingelements during a braking operation, i.e. the time that passes until twotoothing elements are engaged after a braking operation has beentriggered and act counter to one another such that a further rotation ofthe shaft, in particular of the output shaft, is braked or blocked. Alarge number of toothing elements causes a relatively small angularspacing between the individual toothing elements (around thecircumference of the claw-clutch part). Consequently, it is alsopossible for the toothing elements to have only a small materialthickness in the direction of rotation (i.e. in the circumferentialdirection of the claw-clutch part).

In one embodiment according to the invention of the safety brake device,the maximum angular spacing Δ_(max) of mutually adjacent toothingelements of the first claw-clutch part and/or of the second claw-clutchpart is given in accordance with the function Δ_(max)=rps·360°·Δt. Inthis case, the maximum angular spacing (in the circumferentialdirection) is definable according to the invention in a manner dependenton the maximum rotational speed rps and on a predefined braking durationΔt that is to be tolerated in particular at a maximum. In oneembodiment, Δt≤5 milliseconds, in particular Δt≤3.0 milliseconds, veryparticularly Δt≤1.5 milliseconds. In one exemplary embodiment, Δt≤2.8milliseconds. In this way, a particularly quickly reacting brake deviceof the safety brake device can be realized. For example, for anexemplary maximum rotational speed of 83.3 rps (here: persecond—corresponding to 5000 rpm) of a portable circular saw and atolerated maximum braking duration of Δt≤1 millisecond, a maximumangular spacing Δ_(max) of mutually adjacent toothing elements of lessthan or equal to 30° results. The braking durations Δt that are to betolerated at a maximum relate only to the interaction time of the twoclaw-clutch parts, but do not take further time slices—as arise forexample from deceleration caused by triggering the actuator element—into consideration. It is only with the abovementioned short brakingdurations that satisfactory total braking times (including all timeslices from contact, i.e. including decelerations cause by sensors,actuators and the actual braking duration Δt) of the power tool can beachieved, which are less than 10 milliseconds, in particular less than 7milliseconds, very particularly less than 5 milliseconds. It should benoted that the time specifications are each specifications withoutmanufacturing tolerances.

In one embodiment according to the invention of the safety brake device,the number α of the toothing elements of the first claw-clutch partand/or of the second claw-clutch part is given in accordance with thefunction

${\alpha = \sqrt[\gamma]{ɛ/{rpm}}},$

with the maximum rotational speed rpm (here: per minute) and theconstants γ and ε, wherein in particular γ>1.2 and ε>80 000, preferablyγ>1.5 and ε>170 000, and particularly preferably γ>1.7 and ε>300 000. Inthis way, a preferred ratio of the toothing elements can be specifieddepending on the maximum rotational speed and the desired (i.e. maximumtolerable) braking duration Δt.

The following table collates preferred numbers of toothing elementsdepending on a maximum rotation speed rpm (rounded values):

particularly rpm suitable preferred preferred   2500 12 14 16   5000 810 12 10 000 4 6 8 20 000 3 4 5 30 000 2 3 4

In one embodiment according to the invention of the safety brake device,the ratio of the number α of the toothing elements of the firstclaw-clutch part and of the second claw-clutch part (or vice versa) isan integer, in particular 1 or 2 or 3. In an alternative embodiment,this ratio can be 4 or 5. In particular, ratios other than 1 make itpossible to allow in particular manufacturing-related deviations. Forexample, it can be necessary, for production reasons, for theclaw-clutch parts to have different numbers of toothing elements onaccount of different production processes (forging, extrusion,sintering, etc.).

In one embodiment according to the invention of the safety brake device,a maximum width β (as seen in the circumferential direction) of thetoothing elements of the first claw-clutch part and/or of the secondclaw-clutch part is determined depending on the number of the toothingelements. In particular, the maximum width β of the toothing elements(i.e. ascertained in the direction of revolution) of the firstclaw-clutch part and/or of the second claw-clutch part is given inaccordance with the function β=θ·α^(−σ), wherein in particular θ≅218 andσ≅1.311. Thus, it is possible for the toothing elements to have anadvantageous width that is able to be realized easily in a productionprocess. Furthermore, it is possible to ensure that the width of thetoothing elements is chosen such that, with a preferred number of thetoothing elements, the width thereof is not chosen to be too small, suchthat it is possible to avoid any breaking of the toothing elementsduring a braking operation.

The following table collates preferred widths of toothing elementsdepending on the number thereof (rounded values):

Number Width [°] 8 15.0 12 8.7 16 5.8 20 4.1 24 3.2 28 2.6 32 2.3 36 2.140 2.0

As a result of the design according to the invention of the safety brakedevice in terms of a number and distribution of the toothing elements,which are brought into engagement during a braking operation, dependingon the rotational speed of an output shaft of a power tool in which thesafety brake device is used, a particularly advantageous braking actionor braking effectiveness can be achieved taking the robustness, reactiontime, braking time etc. of the brake device into consideration. Inparticular, on account of the configuration according to the inventionof the brake device of the safety brake device, particularly highbraking effectiveness, i.e. a particularly short time between thebraking operation being triggered and the standstill of the machiningtool, can be achieved in a structurally particularly simple manner. Thebrake device reacts particularly quickly after the actuator element hasbeen triggered, in order to avoid or entirely rule out injuries to theoperator in the event of encroachment into the moving machining tool.Furthermore, the brake device of the safety brake device can be realizedin a structurally particularly simple manner and therefore also in aparticularly reliable manner.

Furthermore, the invention relates to a power tool, in particular aportable power tool, in particular a portable circular saw having amachining tool in the form of a circular-saw blade, comprising a safetybrake device according to the invention. In this way, in order to brakea movement, in particular a rotation, of the machining tool, aparticularly short braking time, ascertained between triggering of abraking operation and the stopping of the machining tool (=engagementtime of the claw clutch), is achieved. In particular, this maximumbraking time Δt≤5 milliseconds, in particular Δt≤3.0 milliseconds, veryparticularly Δt≤1.5 milliseconds. Thus, the safety of a user of thepower tool can be increased considerably.

In one exemplary embodiment of the power tool, the latter also has asensor plate, which detects a user approaching or coming into contactwith the machining tool, in particular contact of human skin with themachining tool. Following detection of a user approaching or coming intocontact with the machining tool, electronics of the power tool energizethe actuator element, which triggers a braking operation. In oneexemplary embodiment, the actuator element can be in the form of alifting unit, which actively moves at least one of the two claw-clutchparts of the claw clutch in order to bring the two claw-clutch partsinto engagement with one another during a braking operation and in thisway stop, in particular block, rotation of the shaft. Here, a “liftingunit” is understood to be one or more elements which, upon applicationof activation energy, for example in the form of electric current, arecapable of abruptly expanding axially and abruptly axially moving, inparticular in less than 5 milliseconds, at least one claw-clutch part ofthe claw clutch in order to bring the two claw-clutch parts intoengagement with one another. Such lifting units or other actuatorelements are known to a person skilled in the art from the prior art.

DRAWINGS

The invention is explained in more detail in the following descriptionby way of exemplary embodiments illustrated in the drawings. Thedrawings, the description and the claims contain numerous features incombination. A person skilled in the art will expediently also considerthe features individually and combine them to form useful furthercombinations. Identical reference signs in the figures denote identicalelements.

In the figures:

FIG. 1: shows a perspective illustration of a power tool according tothe invention,

FIG. 2: shows a schematic illustration of a sectional illustrationthrough parts of the power tool together with a safety device accordingto the invention and brake device,

FIG. 3: shows a schematic illustration of a brake device according tothe invention.

FIG. 1 shows a power tool 10 according to the invention, which isrealized as a portable circular saw 10 a. It should be noted that theembodiments should not be understood as being limited to a portablecircular saw 10 a, but rather the technical teachings underlying theembodiments are also transferable in principle to any other power toolsthat appear appropriate to a person skilled in the art, in particularfor example drilling machines, lawnmowers, string trimmers or the like.

The portable circular saw 10 a comprises a first housing, which is inthe form of a motor housing 12, and a second housing 14. The portablecircular saw 10 a has a handle 16 and a base plate 18 for guiding theportable circular saw 10 a. To be supplied with energy, the portablecircular saw 10 a has a grid connection (not illustrated in more detailhere). In an alternative or additional embodiment of the portablecircular saw 10 a, operation of the portable circular saw 10 aindependently of the power grid can also be provided using arechargeable battery.

The motor housing 12 encloses an interior in which at least one motor 22in the form of an electric motor drive is arranged. As illustrated inFIG. 2, the motor 22 drives a machining tool 28 (cf. FIG. 1) in rotationduring a work operation via a motor shaft 24 and a shaft 26, inparticular an output shaft. The machining tool 28 is in the form of asaw blade, in particular of a circular saw blade, here. A saw bladecover 30 prevents contact from being made with the machining tool 28 andprovides protection from chips of a workpiece that are thrown out by themachining tool 28 (cf. FIG. 1).

A safety brake device 32 is provided for braking the machining tool 28as soon as contact or proximity of a human body part, for example ahand, is detected by a sensor 34 of the portable circular saw 10 a. Thesensor 34 is realized by a capacitively measuring sensor in thisexemplary embodiment. The sensor 34 makes it possible to detect a bodypart approaching the machining tool 28 on the basis of capacitivemeasurements (for example by means of an alternating field), wherein,following detection, a detection signal is generated and output to acontrol device of the portable circular saw 10 a (cable connection inFIG. 2 between sensor 34 and electronics 102).

The safety brake device 32 comprises an actuator element 36, which isprovided to trigger a braking operation following detection of a humanbody part coming into contact with or approaching the machining tool 28.Here, triggered by the reception of the detection signal from the sensor34, electronics 102 (not illustrated in more detail here) of the safetybrake device 32 initiate a flow of current through the actuator element36, with the result that the actuator element 36 initiates a brakingoperation in that the actuator element 36 acts on the properfunctionality (i.e. the rotation) of the shaft 26 and brakes or stopsthe latter.

FIG. 2 also shows a first gear wheel 38, which is arranged on the motorshaft 24 and meshes with a second gear wheel 40 arranged on the shaft26. In this way, the first gear wheel 38 and second gear wheel 40 form asafety clutch and a transmission stage. In particular, the safety clutchprotects the motor 22 from damage that can be caused by blocking of themachining tool.

Furthermore, by means of the safety clutch, the mass and energy to bebraked during a braking operation can be reduced in that the motor shaft24 is decoupled from the shaft 26. In this way, a particularly shortbraking time can be allowed. In the exemplary embodiment illustrated,the safety clutch is provided to decouple the motor shaft from the shaft26 when a threshold value of the transmitted torque of at least 5 Nm, atmost 12 Nm, preferably 10 Nm, is exceeded.

The safety brake device 32 also comprises a brake device 42 for brakingthe machining tool 28 driven by means of the motor 22 via the shaft 26when a user approaches or comes into contact with the machining tool 28.The brake device 42 is in the form of an at least two-part claw clutchwith a first claw-clutch part 44 and a second claw-clutch part 46,wherein the first claw-clutch part 44 is arranged on the shaft 26 so asto allow essentially no relative rotation and so as to be axiallymovable. The second claw-clutch part 46 is arranged so as to allowessentially no relative rotation, in particular so as to besubstantially immovable, with respect to the power tool, i.e. withrespect to the motor housing 12. The first claw-clutch part 44 and thesecond claw-clutch part 46 each have more than one toothing element 48,which are provided to be engaged with one another during a brakingoperation (cf. FIG. 3) and in this way to brake, in particular stop,rotation of the shaft 26.

During a braking operation, the first claw-clutch part 44 is movedaxially along the shaft 26 (in the direction 100) in the direction ofthe second claw-clutch part 46. As a result of the axial movement of thefirst claw-clutch part 44 toward the second claw-clutch part 46, thefirst claw-clutch part 44 and second claw-clutch part 46 are coupledtogether, i.e. the clutch is closed. The toothing elements 48 of thefirst claw-clutch part 44 and of the second claw-clutch part 46consequently engage in one another and form a form fit. On account ofthe form fit, a torque directed counter to the rotation of the outputshaft acts between the first claw-clutch part 44 and second claw-clutchpart 46. Consequently, the rotation of the output shaft and of the firstclaw-clutch part 44 is braked, in particular stopped or blocked.

In the exemplary embodiment in FIG. 2, the first claw-clutch part 44 ismoved axially by means of the actuator element 36. The actuator element36 is in the form of a lifting unit here, which, triggered by a flow ofcurrent through the lifting unit, performs a lever movement, wherein thefirst claw-clutch part 44 is moved in the axial direction 100. The levermovement takes place in a time of less than 5 ms, in particular lessthan 1.5 ms.

In FIG. 3, the brake device 42 is illustrated in an enlarged manner andin a manner reduced to the essential components. The brake device 42 hasat least a first claw-clutch part 44 and a second claw-clutch part 46.The two claw-clutch parts 44, 46 have toothing elements 48 between whichrecesses 50 are located in each case. The ratio of the number α of thetoothing elements 48 of the first claw-clutch part 44 to the number α ofthe toothing elements 48 of the second claw-clutch part 46 is one (samenumber, in each case eight). A maximum angular spacing Δ_(max) ofmutually adjacent toothing elements 48 of the first claw-clutch part 44and of the second claw-clutch part 46 is determined depending on amaximum rotational speed of the shaft 26. The maximum rotational speedof the shaft 26 in the exemplary embodiment described is 5000revolutions per minute. The maximum angular spacing Δ_(max) is givenhere in accordance with the function Δ_(max)=rps·360°·Δt, wherein abraking duration Δt to be tolerated at a maximum (from the triggering ofthe actuator element) is intended to be less than 1.5 milliseconds.Accordingly, the resulting maximum angular spacing Δ_(max) of mutuallyadjacent toothing elements 48 of the first claw-clutch part 44 and ofthe second claw-clutch part 46 is 45° in each case.

Furthermore, the number α of the toothing elements 48 of the firstclaw-clutch part 44 and of the second claw-clutch part 46 is given inaccordance with the function

${\alpha = \sqrt[\gamma]{ɛ/{rpm}}},$

with the constants γ=1.377 and ε=79606, such that the resulting number(rounded) is eight. The width β (maximum width in the direction ofrevolution or direction of rotation) of the toothing elements 48 of thefirst claw-clutch part 44 and of the second claw-clutch part 46 isdefined depending on the number (eight) of the toothing elements 48 and,according to the function β=θ·α^(−σ) with θ≅218 and σ≅1.311, is aboutfifteen degrees.

1. A safety brake device for a power tool for braking a machining tooldriven by means of a motor via an output shaft, comprising: at least onebrake device configured as an at least two-part claw clutch, the atleast two-part claw clutch including a first claw-clutch part, and asecond claw-clutch part, wherein: the first claw-clutch part is arrangedon the output shaft so as to allow essentially no relative rotation; thesecond claw-clutch part is configured to allow essentially no relativerotation with respect to the power tool; the first claw-clutch part hasa first plurality of toothing elements; the second claw-clutch part hasa second plurality of toothing elements; the first and second pluralityof toothing elements are configured to engage with one another during abraking operation to stop rotation of the output shaft; and a maximumangular spacing Δ_(max) of mutually adjacent toothing elements of atleast one of the first plurality of toothing elements an the secondplurality of toothing elements is determined depending on a maximumrotational speed of the output shaft.
 2. The safety brake device asclaimed in claim 1, wherein: the maximum angular spacing Δ_(max) of themutually adjacent toothing elements is given in accordance with thefunction rps·360°·Δt=Δ_(max); “rps” is the maximum rotational speed persecond; “Δt”—is a maximum braking duration; and Δt≤5 milliseconds. 3.The safety brake device as claimed in claim 1, wherein a ratio of thenumber of the toothing elements of the first plurality of toothingelements and of the second plurality of toothing elements is an integer,in particular
 1. 4. The safety brake device as claimed in claim 1,wherein: a number α of the toothing elements of at least one of thefirst plurality of toothing elements and of the second plurality oftoothing elements is given in accordance with the function${\alpha = {\sqrt[\gamma]{ɛ/{rpm}}\left\lbrack \lbrack,\rbrack \right\rbrack}};$“rpm” is the maximum rotational speed per minute; “γ” is aconstant >1.2; and “ε” is a constant >80
 000. 5. The safety brake deviceas claimed in claim 1, wherein a maximum width of the toothing elementsof at least one of the first plurality of toothing elements and of thesecond plurality of toothing elements is determined depending on anumber (α) of the toothing elements in the at least one of the firstplurality of toothing elements and second plurality of toothingelements.
 6. The safety brake device as claimed in claim 5, wherein: themaximum width of the toothing elements of the at least one of the firstplurality of toothing elements and of the second plurality of toothingelements is given in accordance with the function β=θ·α^(−σ); θ≅218; andσ≅1.311.
 7. A portable power tool, comprising: an output shaft operablycoupled to a motor; and at least one brake device configured as an atleast two-part claw clutch, the at least two-part claw clutch includinga first claw-clutch part, and a second claw-clutch part, wherein: thefirst claw-clutch part is arranged on the output shaft so as to allowessentially no relative rotation; the second claw-clutch part isconfigured to allow essentially no relative rotation with respect to thepower tool; the first claw-clutch part has a first plurality of toothingelements; the second claw-clutch part has a second plurality of toothingelements; the first and second plurality of toothing elements areconfigured to engage with one another during a braking operation to stoprotation of the output shaft and a maximum angular spacing Δmax ofmutually adjacent toothing elements of at least one of the firstplurality of toothing elements an the second plurality of toothingelements is determined depending on a maximum rotational speed of theoutput shaft.
 8. The safety brake device of claim 2, wherein Δt≤3milliseconds.
 9. The safety brake device of claim 8, wherein Δt≤1.5milliseconds.
 10. The safety brake device of claim 4, wherein: γ>1.5;and ε>170 000
 11. The safety brake device of claim 10, wherein: γ>1.7;and ε>300 000.